The suggestion that sucrose or even glucose ingestion in large
proportions could be the origin of the laxative effect in pigs
and poultry fed sugar cane final molasses (Alvarez 1976;
Entringer etal 1975) has not been a successful
explanation considering that high-test cane molasses, or even
molasses type A and B, have high digestibility indices, in line
with a slower rate of passage of digesta, mainly in the large
intestine (Ly 1977; Ly and Díaz 1979).

Searching for a general comprehensive theory, Cuban
investigations re-examined the chemical composition of sugar cane
molasses in order to determine the factor(s) which could be
directly affecting the rate of passage of digesta and
digestibility of the diet.

In fact, it has been found that although the well known
carbohydrate fraction contained in sugar cane molasses exhibits a
relatively high pre-caecal digestibility (Figueroa et al
1988) very similar to pure sucrose, glucose, and fructose (Ly
1987), a poor pre-caecal disappearance of non-identified organic
substances (NFE - true carbohydrates) present in the molasses
(table 10) has been observed. On the other hand, caecal and
colonic disappearance of these non-identified substances must be
largely due to microbial activity in this area of the
gastrointestinal tract of the pig (Crenwell 1968) hence lowering
even more the dietary energy availability (table 11). In this
connection, some preliminary studies carried out in rats fed
diets containing isolated compounds from non-identified organic
substance from molasses NFE revealed a reduction in faecal dry
matter (Figueroa and Macía 1988) and probably nutrient
digestibility.

There is no doubt that the energy density of sugar cane
molasses diets in terms of gross energy is lower than those of
cereal and grain based diets, basically due to the difference
between the heat of combustion of sucrose and its hexose
components (some 16,5 and 15,3 Kjoules/g respectively) and
amylose and amylopectin (roughly 17,1 Kjoule/g, according to
Nehring and Haenlein (1973). Furthermore, if it is taken into
account that the amount of non- identified organic substances
contained in the different types of sugar cane molasses is
minimum in high-test molasses and maximum in final molasses, it
is logical to expect high values for the digestible energy
content of the former if contrasted with the latter.

Table 10: Digestibility
in pigs of swill obtained from food wastes and other
residues.

------------------
Digestibility up to the rectum,% ------------------

DM

DM

OM

N

Energy

KJ/g

Source

79.8

84.0

83.7

16.16

Grau et al
1976

78.1

82.4

Maylin and
Grau 1977

85.3

87.9

83.6

85.4

16.51

Maylin and
Cervantes 1982

81.6

82.2

82.3

12.25

Maylin 1983

80.7

76.8

79.7

14.37

González et
al 1986

78.4

76.0

77.0

Domínguez
et al 1988

--------------------
Digestibility up to the ileum, % --------------------

71

65.2

68.9

Domínguez et
al 1988

Table 11: Apparent
digestibility of energy sources in the pig.

----------
Digestibility, % ----------

Up to ileum

Up to rectum

Source of
data

Dry matter

- Sucrose

98.3

100.0

Ly et al
1987

- Cassava
starch

87.0

100.0

Figueroa et
al 1989

- Molasses
type A

84.0

94.0

- High-test
molasses

83.5

95.9

Figueroa et
al 1987

- Final
molasses

63.0

81.0

Díaz et
al 1984

Carbohydrates

- Sucrose

98.3

- Cassava
starch

99.0

- Molasses
type A

96.0

- High-test
molasses

96.5

- Final
molasses

83.0

Non-identified
Organic substances

- Sucrose

- Cassava
starch

- Molasses
type A

14.0

79.0

- High-test
molasses

0.0

28.9

- Final
molasses

51.0

70.0

One of the consequences of the apparent absorption from the
gastrointestinal tract of certain fractions of the non-identified
organic substances could be the increased calorific value of the
urinary nitrogen in pigs (table 12). These observations could
otherwise explain the decrease in metabolizable energy values of
sugar cane molasses, even more pronounced in final than in high-
test molasses. A net decrease in metabolizable to gross energy
ratio has been observed in chickens fed increasing levels of
sugar cane final molasses in the diet (Alvarez 1977). In this
connection it could be possible that in poultry as in pigs the
depression of metabolizable energy in diets based on sugar cane
molasses depends not only on the level but on the type of this
feed to be utilized, perhaps due to the level of non-identified
organic substances contained in the molasses.

The role of the microbial activity in the gastrointestinal
tract might be another factor that influences digestible and
metabolizable energy values of sugar cane molasses for pigs and
poultry. Experiments conducted in this sense appear to indicate a
major fermentative action in crop and caeca of chickens (Alvarez
and Ly 1975) if compared to what is occurring in the alimentary
canal of pigs (table 13). Furthermore, high-test molasses can
result in a greater rate of volatile fatty acid production in the
caecum and colon of pigs than final molasses.

Table 13: Calorific
value of the urinary nitrogen from pigs fed diets based
on sugar cane molasses or cereals (1).

Source of
energy

Calorific
value, KJ/g urinary N

Cereal

41.46

Sucrose

53.83

High-test
molasses

58.86

Molasses type
A

62.96

Molasses type
B

71.33

Final
molasses

79.34

(1) Data from 28 balance trials
with 150 growing pigs (30-50 kg)

Source of data: Ly (1988)

Some metabolic profiles of pigs fed sugar
cane molasses

Digestion of sucrose and therefore fructose utilization by
pigs and poultry is one of the immediate consequences of a
feeding system based on sugar cane molasses or other sugar cane
derived feed. In the pig, earlier experiments carried out to
study the fate of fructose utilization in growing animals fed
either fructose or swill plus sugar cane final molasses indicated
that some 10 % of dietary fructose can escape from absorption in
the pre-caecal areas (see Ly 1987) or from tissue metabolism
after absorption thus being excreted through the kidneys in
levels accounting for 3 to 5 % of daily feed intake of this
hexose (Ly and Macía 1979). This fructosuria could have its
origin in an absence of renal threshold in the pig. The presence
of fructose in caecal contents of chickens fed sugar cane final
molasses could be caused not only by an incomplete absorption in
the small intestine like in pigs, as suggested by Alvarez (1976),
but also by excretion in the urine.

On the other hand, fructosuria seems not to be an effect
solely of sugar cane final molasses intake, since this phenomenum
is also present in diets formulated with sucrose as the only
source of carbohydrate (Ly et al 1988).

The excretion of DL-lactate in the urine has been found in
pigs fed sugar cane feeds, together with a persistent fructosuria
(Ly et al 1988a; Ly et al 1988b). Besides, the
concentration of DL-lactate tends to reach a maximum and urinary
pH value a minimum. Urinary DL-lactate does not seem to be an
important energy loss but an indicator of a possible metabolic
modification in pigs and possibly farm birds fed sugar cane
molasses. In fact the origin of DL-lactate could be due to the
fermentation in the gastrointestinal tract, mainly in the crop of
the chickens (Valarezo and Preston 1973; Alvarez and Ly 1975) or
from the absorptive process both in pigs (Mansford 1965;
Talafantova and Kolinska 1977; Bjorkman et al 1984) and
chickens (Leveille et al 1970). On the other hand, a
noteworthy production of lactic acid has been found from fructose
injected intravenously in pigs (Ly etal 1988a) and
chickens (Leveille et al 1970). In fact, fructose and not
glucose has the property of elevating DL-lactate in the blood
after intravenous tolerance tests carried out in man (Cook 1970).

Another feature to be considered concerning carbohydrate
metabolism in pigs and poultry fed sugar cane feeds might arise
from an altered acid-base status together with an impaired
glucose tolerance test (Ly et al 1981; Rodríguez et al
1985). In fact, changes in the characteristics of the urine of
the pigs may be related to changes in the pattern of feed intake
and demineralization processes in the bones (Ly 1987). The
observed phenomena related to the feeding of pigs and chickens
with sugar cane molasses could give rise to several hypotheses in
order to explain the relationship between the different
components of the feeding formula which contributes to neutralize
these considerable events and even improves this intensive pig
and poultry production model.

Some conclusive remarks

The strategy for a new pig and poultry production system in
the tropics can successfully face the challenge of applying new
technologies in animal feeding. The Cuban feeding systems have in
common the use of a liquid feed with variable amounts of sucrose,
where the protein source may not necessarily be a conventional
one. In this respect, the system can serve as a model of how to
use local feed resources widely available in the tropics for pigs
and poultry. At the same time, the model avoids the competition
for resources useable by humans, as is the case when cereal
grains are used in animal feeding.

In the development of such feeding systems, research into
nutritional physiology and biochemistry aspects of the system is
not just an academical exercise but a very useful tool of how to
improve animal feed efficiency by opening new frontiers of
knowledge.

Acknowledgements

I am greatly indebted to the organizers of the Training Course
Animal Production in Developing Countries, Dr P H Petersen, Dr F
Dolberg and Dr T R Preston for permitting me to publish the
course lectures.

I wish to express my thanks to the librarians of the Swine
Research Institute, Dr Maria del Careen Montpeller, Mrs Juana
Camacho and Mrs Nancy González. I am also grateful to the
librarians of the Institute of Animal Science, Dr Laysi Brito,
Mrs Caridad Cruz and Mrs Milagros Alvarez, for their invaluable
help and assistance in literature searching. Gratitude is also
expressed to Mr M Lorenzo.

My special thanks to my colleagues Dr Miriam Ribas, Dr Dulce
Maria Vento and Dr Lidia González, from the Editorial Board of
the Cuban Journal of Agricultural Science for their skillful
advise and help concerning the English manuscript.

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